There isn't a specific 'organ' - Snakes usually have a row of heat-sensitive 'pits' (or tiny holes) arranged around the top edge of their mouth.
Heat pit
They would taste the air, flicking out their toungue or if they were hunting for prey, some snakes have a sort of heat detector which detects the heat of animals.That's correct, but for the sake of specificity, I will say that it the snakes that have a heat-sensing "pit" organ are Pythonidae (Aspidites was recently shown to have a similar organ on its upper lip), some Boidae, and Crotalinae (pit vipers).
Snakes have special organs (pit organ) between their eyes and nose that can sensor infrared's radiation. With this organ it enables it to detect animals that have heat trapped in them (example: mice, birds)
heat sensor
Thermoreceptors in snakes are found in two spots on either side of the nose called a pit. The pit is seen in pit vipers and boa snakes. The snakes can actually use the amount of heat detected from each side and use that to determine where they prey is and how close it is. .
pit organ
Pit Organ
pit organ
I'm sure there are many, I can only think of a pit-viper. They have an organ that can sense heat. It is located between the eyes and nostrils. This organ is extremely sensitive to even the smallest temperature changes with 7,000 nerve endings.
the pit is a heat sensing organ due to poor visibility of a snakes eyes, therefor lets them see the "body heat" of the animal and acting as a second set of "eyes"
Snakes cannot produce their own heat because they are coldblooded.
Any device that detects smoke or heat and that sounds an alarm.